CIRCULATION IN THE BLOOD-VESSELS 8/ 



and thus in the amount of blood driven into the arm. Compress the 

 brachial vein above the elbow ; the swelling of the arm due to reten- 

 tion of blood is at once shown. 



Plethysmographs for the kidney, spleen, and other organs may be 

 also studied (see Fig. 72, p. 88). The principle of their action is the 

 same as that used for the arm, but the form is adapted to each 



FIG. 70. Lud wig's stromuhr. a, a', Cannulas for tying into cut artery ; 6, 

 block on which the part c rotates around the axis, d ; e, reservoir contain- 

 ing oil ; e', reservoir containing defibrinated blood ; /, aperture for filling 

 reservoirs, closed by cork, g. 



particular organ. The glass cover as well as the gap (g) in the 

 instrument through which the vessels and duct pass are made air-tight 

 by vaseline. 



In Mosso's original instrument, and in Roy's oncometer, which 

 works on a similar principle, the apparatus was filled with fluid (water, 

 oil) ; but this is unnecessary, air-transmission to a piston recorder or 

 tambour giving quite as accurate results. 



